Reactivity of cobalt(III) amine-thiolate complexes with terminal and bridging thiolate functions towards hydrogen peroxide

The reactivity of Co-III amine-thiolate complexes with terminal and bridging thiolate functions towards oxidizing agents has been investigated. The mononuclear (CON3S3)-N-III complex [Co-III(L-1)] (2) (H3L1 represents the hexadentate ligand N,N',N " -Tris(2-thio-benzyl)-1,1,1-tris(aminomethyl)ethane) featuring three terminal thiolate ligands, and the binuclear N3CoIII- (mu -S)(3)(CoN3)-N-III complex [Co-2(III)(L-2)](3+) (4) (H3L2 = N,N',N " -Tris-[2-thio-3-aminomethyl- butyl-benzyl] 1,1,1-tris(aminomethyl)ethane) featuring three bridging thiolates were selected. Hydrogen peroxide was the oxidizing agent. Whereas the thiolato-bridged complex 4 is resistant towards oxidation by hydrogen peroxide 2 undergoes a ligand-based oxidation reaction to give the amine-sulfinate complex [Co(L-1)] 5, where all three terminal thiolates have been oxidized to sulfinates without gross structural changes of the parent complex 2. In contrast to 4, the cyclic voltammogram of 2 reveals an irreversible oxidation wave at E = +0.52 V vs SCE which can be attributed to a ligand-centered oxidation reaction. 4 and 5 have been structurally characterized by X-ray crystallography.